from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A polyhedron having 20 faces.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A polyhedron with twenty faces.
- n. A regular icosahedron: one of the Platonic solids, all of whose faces are regular triangles
from the GNU version of the Collaborative International Dictionary of English
- n. A solid bounded by twenty sides or faces.
from The Century Dictionary and Cyclopedia
- n. A solid bounded by twenty planes.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. any polyhedron having twenty plane faces
The icosahedron is another of the five regular, or Platonic, bodies having all their sides, angles, and planes similar and equal.
Then, about 10 years ago, the mathematician Reidun Twarock developed a more general theory of the geometry of viruses based on the symmetries of the icosahedron, but using shapes in six dimensions, not three.
I've rolled the icosahedron and painted a few miniatures myself so it only raises my charisma to be accepted by that culture.
The company receives more than 1 million applications a year and identifies the top candidates through a rigorous screening process that analyzes SAT scores, grade-point averages and their performance on tests with such questions as: "How many different ways can you color an icosahedron with one of three colors on each face?"
Join five equilateral triangles together and you have the first part of an icosahedron C.
Only five shapes fit the bill: the tetrahedron, the cube, the octahedron, the icosahedron and the dodecahedron, the quintet known as the Platonic solids since Plato wrote about them in the Timaeus.
The octahedron can be made from four cards and an icosahedron with ten of them.
The tetrahedron was fire, the cube earth, the octahedron air, the icosahedron water and the dodecahedron the encompassing dome.
This set of five polyhedra came with the faces already numbered, to make it easy to see that there were 12 sides on a dodacahedron, or 20 on an icosahedron, which made them easy to use as dice.
George Hart has nice pictures including an icosahedron as well.